1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a technology which is effectively applicable to a flexible printed wiring board provided with light-emitting diodes mounted thereon.
2. Description of the Related Art
A liquid crystal display device (also referred to as liquid crystal display module) of a thin film transistor (TFT) system, which includes a compact liquid crystal display panel, is widely used as a display part of portable equipment such as a mobile phone.
FIG. 10 is an exploded perspective diagram illustrating a schematic configuration of a conventional liquid crystal display device for a mobile phone.
As illustrated in FIG. 10, the conventional liquid crystal display device includes a liquid crystal display panel (LCD) and a backlight (B/L) for illuminating the liquid crystal display panel (LCD).
The backlight (B/L) includes a light guide plate 6 which has a substantially rectangular shape similar to a plane shape of the liquid crystal display panel (LCD), white light-emitting diodes (light sources; hereinafter, referred to as LEDs) 8 disposed on a side surface (light incident surface) of the light guide plate 6, a reflection sheet 7 disposed on a lower surface (surface on a side opposite to the liquid crystal display panel side) of the light guide plate 6, an optical sheet group 5 disposed on an upper surface (surface on the liquid crystal display panel side) of the light guide plate 6, and a molded resin frame (hereinafter, simply referred to as mold) 10. The optical sheet group 5 is formed by including, for example, a lower diffusion sheet, two lens sheets, and an upper diffusion sheet.
In the conventional liquid crystal display device, the optical sheet group 5, the light guide plate 6, and the LEDs 8 are disposed inside the mold 10 in the order as illustrated in FIG. 10. The reflection sheet 7 is disposed below the mold 10.
Further, the liquid crystal display panel (LCD) includes a pair of glass substrates (2a and 2b), an upper polarizer 1 attached to an upper surface (display surface) of the glass substrate 2a, and a lower polarizer 3 attached to a lower surface (surface on the backlight side) of the glass substrate 2b. 
The glass substrate 2b is provided with a semiconductor chip (DRV) mounted thereon which constitutes a driver or the like. Note that, on the glass substrate 2b, a flexible printed wiring board for supplying a control signal or the like to the semiconductor chip (DRV) is also mounted, however, the flexible printed wiring board is not illustrated in FIG. 10.
Patent Document which discloses the related art of the present invention is JP 2007-25484 A.
FIG. 11 is a cross sectional diagram illustrating a main part of the conventional liquid crystal display device, in which the flexible printed wiring board (FPC) is mounted on the glass substrate 2b. Note that the mold 10 is not illustrated in FIG. 11. Further, FIG. 12 is a plan view illustrating a developed state of the flexible printed wiring board (FPC) illustrated in FIG. 11.
As illustrated in FIG. 12, the flexible printed wiring board (FPC) includes a main body part 20 on which a connection part 21 for connection to the glass substrate 2b and a connection part 22 for external connection (for example, to a mobile phone) are formed, an LED substrate 24 on which the LEDs 8 are mounted, and a connection substrate 23 for connecting the main body part 20 and the LED substrate 24 to each other. Here, the main body part 20 and the LED substrate 24 are each formed of a double-sided flexible printed wiring board, and the connection substrate 23 is formed of a single-sided flexible printed wiring board.
Further, as illustrated in FIG. 11, the connection substrate 23 is folded. As a result, a plurality (four in this case) of the LEDs 8 mounted on the LED substrate 24 are disposed within the mold 10 (not shown) from below the mold 10.
FIG. 13 is a diagram for describing a wiring pattern on the connection substrate 23 and on the LED substrate 24 illustrated in FIG. 11.
In the liquid crystal display device provided with the flexible printed wiring board (FPC) illustrated in FIG. 11, the four LEDs 8 mounted on the LED substrate 24 are driven in parallel with one another. Accordingly, on the connection substrate 23 and on the LED substrate 24 illustrated in FIG. 11, a common anode line (AN) for supplying an anode voltage to all the (four in this case) LEDs 8 and four cathode lines (CN1 to CN4) for supplying a cathode voltage to each of the four LEDs 8 are formed.
In this case, on the connection substrate 23, the anode line (AN) and the four cathode lines (CN1 to CN4) may be wired such that those lines do not intersect with one another.
Meanwhile, on the LED substrate 24, it is necessary to connect the four cathode lines (CN1 to CN4) to each of cathode electrodes (CDE) of the four LEDs 8 while connecting the anode line (AN) to anode electrodes (ADE) of the four LEDs 8. As a result, the anode line (AN) intersects with three of the cathode lines (CN2 to CN4), and hence the LED substrate 24 needs to be a double-sided printed wiring board.
As a result, as illustrated by the arrow A of FIG. 11, the LED substrate 24 which is formed of a double-sided printed wiring board is increased in thickness to exceed the thickness of the reflection sheet 7, and the excess of the LED substrate 24 is formed downwards the reflection sheet 7 due to the difference in thickness, with the result that it has been difficult to reduce the thickness of the liquid crystal display device.